#coding:utf-8
score = int (input("请输入一个分数:"))
if 100 >= score >=90:
    print ('A')
if 90 >= score >=80:
    print ('B')
if 80 >= score >=60:
    print ('C')
if 60 >= score >=0:
    print ('D')
if score <0 or score >100:
    print ('输入错误！')

